1. Field of the Invention
This invention relates to the field of equipment used to measure calorimetric flammability characteristics, particularly the heat emission, of materials such as plastic rods, foam, films and products made from fibers, such as paper and textile structures, especially fabrics.
Heat emission is a major hazard in uncontrolled burning, all too often causing death, serious injury, and extensive damage, particularly from accidental fires. Rate of heat emission determines whether a material will self-extinguish once ignited, because a sufficient rate of heat feedback is necessary to maintain burning, particularly of a fabric. The extent to which the flammability hazard of a material can be understood and eventually be minimized is dependent on our ability to measure heat emission accurately. In addition to the important consideration of safety, the amount of heat emitted and the rate of heat emission can indicate more precisely than any other factors the progress and the completeness of the burning process.
2. Description of the Prior Art
Despite the importance of being able to make meaningful calorimetric measurements in order to understand the burning characteristics of materials, various types of such measuring equipment heretofore provided have had many disadvantages and shortcomings. Arrangements for monitoring burning have depended on measuring the heat transferred to a specific target or to a relatively large heat sink surrounding the burning sample. In the former case, the result is strongly dependent on the location of the target with respect to the flame, an arbitrary as well as variable factor. Using an enveloping heat sink (e.g., as in the form of a labyrinth) requires imposing artificial restraints upon the testing environment such as forced air flow, limited sample size, and restricted freedom of choice of test conditions.
The other general type of arrangement has allowed the heat to remain in the gas stream flowing away from the burning material, and provided for this heat to be measured by following the temperature rise of the gas with a detector that is an insignificant heat sink. But calorimetry based on such gas temperature measurements has not been of practical value, since it requires that the air-flow rate be kept constant, thus imposing unnatural and undesirable restrictions. In summary, devices which have depended on heat transfer have inherent complications which inhibit their use for the study and evaluation of, for example, burning textiles. Direct measurement of emitted heat would be preferable to indirect measurement involving transferred heat. Combustion calorimeters also have the drawback of burning the material under highly artificial conditions as compared to conditions relating to the natural, self-sustained flaming of organic solids. Such artificial conditions confine the spatial configuration and impose an unnatural atmosphere, casting doubt and uncertainty upon the interpretation and significance of results.